The invention relates generally to the field of integrated circuit fabrication and, in particular, to improved metallization methods useful in the production of semiconductor devices.
During the manufacture of integrated circuits, such as semiconducting devices, various conductive and insulative layers of material are deposited on a substrate to provide circuits and interconnects between the circuits. As integrated circuits continue to shrink in size and become more powerful, newer and better manufacturing techniques are devised to improve their performance.
It is desirable for the metallization process to provide surfaces that have high reflectivity. Reflectivity is an indication of the surface roughness, or smoothness, as determined by the amount of light reflected from the surface. Surfaces with a low reflectivity are typically rougher than surfaces of the same material that have a high reflectivity. The reflectivity is expressed in terms of a percentage, based on the intensity of the reflected light compared to the intensity of the incident light. A highly reflective surface tends to be easier to planarize using a process such as chemical mechanical polishing.
Metal layers that are electroplated on sputtered barrier and seed layer systems typically exhibit a high degree of surface roughness. This is especially true for copper layers that are electroplated on top of a tantalum nitride, tantalum barrier layer and copper seed layer that are deposited using a self ionized plasma sputter process. High surface roughness of the electroplated copper layers manifests itself as a relatively low reflectance, which condition is also called haze, which in other words is a reflectance that is below about seventy percent.
Self ionized plasma deposited barrier seed layer also typically exhibit a high degree of instability. As the layer self anneals, the mean sheet resistance and sheet resistance uniformity tend to change for several hours or so after deposition. The reflectivity problems and resistivity problems, described above, adversely affect later processes such as the chemical mechanical polishing step, and tends to impact line resistance and electromigration properties of the layer.
There exists a need, therefore, for improved methods of manufacture to enhance the uniformity of the underlying layers and increase the reflectance of the plated layers, while at the same time maintaining adequate barrier layers between the electroplated layer and the substrate.
The above and other needs are met by a method for creating a highly reflective surface on an electroplated conduction layer. A barrier layer is deposited on a substrate using a self ionized plasma deposition process. The barrier layer has a thickness of no more than about one hundred angstroms. An adhesion layer is deposited on the barrier layer, using a self ionized plasma deposition process. A seed layer is deposited on the adhesion layer, also using a self ionized plasma deposition process, at a bias of no less than about one hundred and fifty watts. The combination of the barrier layer, adhesion layer, and seed layer is at times referred to herein as the barrier seed layer. The conduction layer is electroplated on the seed layer, thereby forming the highly reflective surface on the conduction layer, where the highly reflective surface has a reflectance of greater than about seventy percent.
In another aspect the invention provides a method for creating a highly reflective surface on a metal layer system having a substantially constant mean sheet resistance. A barrier layer is deposited on a substrate using a self ionized plasma deposition process. The barrier layer has a thickness of no more than about one hundred angstroms. An adhesion layer is deposited on the barrier layer, using a self ionized plasma deposition process. A seed layer is deposited on the adhesion layer, also using a self ionized plasma deposition process, at a bias of no less than about one hundred and fifty watts. A conduction layer is electroplated on the seed layer, thereby forming the highly reflective surface on the conduction layer, where the highly reflective surface has a reflectance of greater than about seventy percent.
An advantage of the invention is that the electroplated conduction layer deposited on the barrier seed layer formed as described above exhibits a significantly higher reflectance, or in other words much lower surface roughness, than an electroplated conduction layer deposited on a barrier seed layer formed by prior art processes. Furthermore, the self ionized plasma deposited barrier seed layer as described above tends to be more uniform and stable over time with respect to the mean sheet resistance of the layer, which may indicate a lower degree of self annealing. Because the mean sheet resistance of the barrier seed layer is relatively constant over time, the amount of elapsed time between the barrier seed layer deposition and the electroplating step is less critical, and may be substantially shorter. The process is also tends to reduce electromigration within the electroplated conduction layer.